Time-Dependent Degradation of Imipenem in Aqueous Solution and Its Impact on Antibacterial Activity.

Background/Objectives: Imipenem, known as a carbapenem, is widely used in combination with Cilastatin to treat severe bacterial infections. Imipenem is a β-lactam antibiotic with potent antibacterial activity but a relatively unstable chemical structure. Due to these structural characteristics, it may degrade or undergo structural changes over time in aqueous solutions. Methods: In this study, Imipenem was investigated for its structural stability over time in aqueous solution at 37 °C. Structural changes in the Imipenem/Cilastatin solution were confirmed by HPLC-DAD at the maximum absorbance wavelength. Results: Imipenem undergone progressive degradation and structural transformation for the dimerization, while Cilastatin remained stable under the same conditions. LC-Q-TOF/MS confirmed the formation of a dimeric Imipenem species after prolonged incubation. Antibacterial activity showed that Imipenem was effective against P. carotovorum regardless of the dissolution times. However, Imipenem solution after 24 h with chemical degradation exhibited significantly decreased effects against E. coli and P. aeruginosa. Conclusions: Accordingly, the patterns of metabolite changes in Imipenem and Cilastatin were characterized according to concentration and dissolution time, and the corresponding antibacterial activities against different bacterial strains were compared.